Dairy cows are significant investments for dairy farmers, and enormous efforts, such as animal breeding and artificial insemination, have been and continue to be invested in ensuring that the animals have high and sustained productivity, and that the milk produced are of high quality. A successful breeding family is the Holstein line derived from Carlin-M Ivenhoe Bell. More than 25% of the highest total performance index Holstein bulls in the United States are progenies of this individual.
Traditional breeding techniques involve the studying of sire progenies, and evaluating their milk production ratings (transmitting abilities) to guide further breeding. This standard technique requires years to evaluate the true genetic value by progeny testing each bull. Many cows must be bred and give birth to offspring. The females must be raised, bred, allowed to give birth and finally milked for a length of time to measure their phenotypic traits.
Furthermore, selection based purely on phenotypic characteristics does not efficiently take into account genetic variability caused by complex gene action and interactions, and the effect of the environmental and developmental variants. There is thus a need for a method of genetically evaluating cattle to enable breeders to more accurately select animals at both the phenotypic and the genetic level.
Marker-assisted selection can lower the high cost of progeny testing currently used to improve sires, since young bull progeny could be evaluated immediately after birth, and young bulls that are determined by genetic testing to have undesirable markers would never be progeny tested or even prior to birth, for the presence/absence of the marker. Therefore, there is also a need for genetic markers for improved milk production traits.